U.S. patent number 3,803,433 [Application Number 05/227,072] was granted by the patent office on 1974-04-09 for permanent magnet rotor synchronous motor.
This patent grant is currently assigned to General Time Corporation. Invention is credited to Michael J. Ingenito.
United States Patent |
3,803,433 |
Ingenito |
April 9, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
PERMANENT MAGNET ROTOR SYNCHRONOUS MOTOR
Abstract
A synchronous self-starting timer motor having a disc shaped
rotor with an annular ring of permanently magentized poles about
the pheriphery therof. The magnetized poles are of alternately
opposite polarity with the magnetic fields generated thereby being
substantially perpendicular to the plane of the rotor. The stator
includes a core having at least one pole pair which defines an
axial air gap through which the magnetized annular pole portion of
the rotor passes. The stator also has an energizing winding which
induces an alternating or pulsating flux field in the core of the
stator which field co-acts with the field of the rotor to drive the
rotor at a speed proportional to the frequency of the flux field.
The rotor has a low moment of inertia, is light in weight and has a
large magnetic working area so that the synchronous motor is
capable of generating high torque at a low input power level.
Inventors: |
Ingenito; Michael J. (New York,
NY) |
Assignee: |
General Time Corporation (Mesa,
CA)
|
Family
ID: |
22851638 |
Appl.
No.: |
05/227,072 |
Filed: |
February 17, 1972 |
Current U.S.
Class: |
310/156.35;
318/400.09; 318/400.24; 310/163; 331/158; 310/162; 310/268;
331/116R; 368/204; 968/553 |
Current CPC
Class: |
G04C
15/00 (20130101); H02K 21/24 (20130101) |
Current International
Class: |
H02K
29/00 (20060101); H02K 21/24 (20060101); H02K
21/12 (20060101); G04C 15/00 (20060101); H02k
021/12 () |
Field of
Search: |
;310/46,156,162-164,268
;58/23,23A ;318/138,254 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Duggan; D. F.
Attorney, Agent or Firm: Pennie & Edmonds
Claims
1. A synchronous motor comprising:
a disc shaped rotor comprised of a low density material of high
retentivity and having a low moment of inertia and a large magnetic
area to provide a high output relative to the moment of inertia
thereof, said magnetic area including an annular ring of
permanently magnetized poles extending through the thickness and
about the periphery thereof, each of said poles being magnetized
axially and having a pole of opposite polarity positioned
contiguously on each side thereof, and
a stator including a core and an energizing winding, said core
having at least one pole pair which defines an axial air gap
through which passes the permanently magnetized annular portion of
said rotor, said energizing winding being coupled to said stator
core for providing an energizing alternating flux field in said
core, said flux field passing between said stator poles through
said rotor substantially perpendicular to the plane of said rotor,
the magnetic fields generated by said rotor poles passing through
said stator substantially perpendicular to the surface of said
2. The motor of claim 1 wherein said annular magnetized poles of
said rotor
3. The motor of claim 2 wherein the rotor material consists of
barium
4. The motor of claim 2 wherein said stator has only one stator
pole pair.
5. The motor of claim 2 wherein said stator core includes a pair of
complementary pole pieces, said pole forming a plurality of pole
pairs with each pole pair having the approximate configuration of
said rotor
6. The motor of claim 5 wherein said pole faces are aligned
co-axially with
7. A battery operated self-starting synchronous timer motor for
powering an automobile clock comprising:
a disc shaped rotor comprised of a low density material of high
retentivity and having a low moment of inertia and a large magnetic
area to provide a high output relative to the moment of inertia
thereof, said magnetic area including an annular ring of
permanently magnetized poles extending through the thickness and
about the periphery thereof, each of said poles being magnetized
axially and having a pole of opposite polarity positioned
contiguously on each side thereof; and
a stator including a core and an energizing winding, said core
having at least one pole pair which defines an axial air gap
through which passes the permanently magnetized annular portion of
said rotor, said energizing winding being coupled to said stator
core for providing an energizing alternating flux field in said
core, said flux field passing between said stator poles through
said rotor substantially perpendicular to the plane of said rotor,
the magnetic fields generated by said rotor poles passing through
said stator substantially perpendicular to the surfaces of said
8. The motor of claim 7 wherein said annular magnetized poles of
said rotor
9. The motor of claim 8 further comprising circuit means for
providing an AC energizing signal to said energizing winding, said
circuit means including a crystal controlled oscillator, a
frequency divider means for dividing the frequency of the output of
said oscillator, and drive means
10. The motor of claim 8 wherein said stator core includes a pair
of complementary pole pieces, said pole pieces forming a plurality
of pole pairs with each pole pair having the approximate
configuration of said rotor poles.
Description
BACKGROUND OF THE INVENTION
This invention relates to synchronous electric motors and, more
specifically, to very inexpensive self-starting synchronous motors
having high efficiency while requiring low power input. One use of
the self-starting synchronous motor of this invention is for
driving continuously a digital or direct read clock mounted in an
automobile dashboard wherein the power input for the motor is from
the customary automobile battery.
Synchronous timer motors have been used extensively in electric
clocks for some time because of the simplicity of such motors and
the accuracy of the rotational frequency at the output thereof.
Complementing this is the fact that the typically low output torque
of minature synchronous motors is well suited to clocks which do
not require high torque operating levels. In construction, prior
timer or clock motors have often been exceedingly simple. The
stator normally includes an energizing winding in the form of a
simple concentrically wound coil which surrounds part of a magnetic
circuit, designated the core, which distributes the generated
magnetic flux with respect to a rotor. The rotor structure has
taken many forms but can be a simple permanent magnet disc
polarized to have alternating north and south poles about its
periphery. The rotor is rotatably positioned with respect to the
stator core such that the stator core and the rotor define a radial
air gap through which the flux induced in the core passes. Because
of the simple structure of such synchronous timer motors, they are
easily manufactured and produced in large numbers resulting in a
very low cost per unit. These motors, however, have been
notoriously inefficient. For example, the efficiency of prior timer
motors has normally been less than 1 percent, although, in some of
the better grade motors having a more complex structure, the
efficiency has been 2 percent or greater, an example of which is
the motor disclosed in U.S. Pat. No. 3,469,131, issued Sept. 23,
1969 and which is assigned to the same assignee as is the present
application. However, the motor of the stated patent is relatively
expensive and for the same volume or size, does not have the torque
capabilities as the motor disclosed herein.
Over the years battery powered clocks have been developed and are
now very popular. These clocks generally operate by sustaining the
reciprocating or oscillatory motion of a balance wheel, tuning
fork, or pendulum which in turn mechanically drives the hands of
the clock. A simple low power transistor oscillator circuit is
typically utilized to sustain the reciprocating or oscillatory
motion and, consequently, the low energy drain from the clock
battery has permitted battery powered clocks to operate for months
without requiring a change of battery.
Synchronous motors such as disclosed in the aforementioned U.S.
Pat. No. 3,469,131, have been successfully used in battery powered
clocks. However, as explained above, the motors are relatively
expensive and do not have the capabilities necessary for rugged,
low power applications. Accordingly, there has been a need for an
efficient primary source of rotational energy so that the need for
converting reciprocating motion into rotary motion can be
eliminated. The converting of reciprocating motion to rotary motion
involves added parts and steps in the assembling process thereby
resulting in added cost of producing timepieces. Even more costly
and complex is the mechanism in automobile clocks for converting
intermittent reciprocating motion to a relatively smooth and
uniform rotational motion. The use of this mechanism in automobile
clocks has often resulted in automobile clocks keeping inaccurate
time because the shock and the temperature and vibrational extremes
normally experienced by the winding spring and associated parts of
these clocks produced nonlinear torque outputs. The motor of this
invention with its associated electronics eliminates the complex
horology features of present automobile clocks such as, the
hairspring, the balance wheel, the main spring rewind mechanism,
etc. Moreover, this motor provides the torque necessary to drive
displays other than conventional indicating hands, such as, for
example, digital clock drums.
It therefore is an object of this invention to provide a simple,
and efficient synchronous motor for powering battery operated
clocks.
It is another object of this invention to provide an efficient,
continuously operating source of rotational energy for automobile
clocks in which the source of rotational energy is a self-starting
synchronous timer motor which requires a low input power level.
SHORT STATEMENT OF THE INVENTION
Accordingly, this invention relates to an efficient synchronous
motor for producing a relatively large output torque at a low power
input level. The motor includes a stator having a core with at
least one pole pair and an energizing winding coupled to the core
to generate an alternating or pulsating flux field in the core for
rotationally driving a rotor. The rotor is a disc having an annular
ring of permanently magnetized poles about the periphery thereof.
The magnetized poles are of alternately opposite polarity with the
magnetic fields generated thereby being directed substantially
perpendicular to the plane of the disc and parallel to the flux
lines induced in the stator core by the stator windings. The
annular magnetized portion of the rotor passes through an axial air
gap which is defined by the stator pole pair. The rotor has a low
moment of inertia and is lightweight with the magnetized portions
thereof providing a large magnetic working area having a high
retentivity. Consequently, the motor is capable of generating a
high torque at a low power input level.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of this invention will be
more fully understood from the following detailed description of
the preferred embodiment, the appended claims and the accompanying
drawings in which:
FIG. 1 is a plan view of the self-starting synchronous timer motor
of this invention showing the rotor positioned in an axial air gap
defined by the stator core;
FIG. 2 is an end view of the synchronous motor showing the annular
magnetized portion of the rotor;
FIG. 3 is a perspective view of the rotor illustrating the annular
ring of magnetic poles at the outer periphery thereof;
FIG. 4 is a partial plan view of the rotor and stator assembly
showing the relative endwise configuration of the stator with
respect to the rotor;
FIG. 5 is a side section view of the self-starting synchronous
timer motor of this invention with the stator having a plurality of
pole pairs;
FIG. 6 is a detailed illustration of the stator pole structure of
the synchronous motor of FIG. 4; and
FIG. 7 is a schematic diagram of the circuit for driving the
synchronous motor of this invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Refer now to FIG. 1 which shows the preferred embodiment of the
self-starting synchronous motor of this invention. The stator 11
includes a core 13 and an energizing winding 21. The core 13
includes two complementary annealed iron plates 15 and 17 which are
preferably formed by a stamping process. In order to conserve space
and to provide more efficient coupling with respect to energizing
winding 21, the winding support legs 16 of the core plates 15 and
17 are offset with respect to each other as is more clearly
illustrated in FIG. 2. The legs are positioned side-by-side and are
spot welded to form a unitary stator core. Since the leg portions
of the core are positioned side-by-side, the cross sectional area
of the core as it passes through the winding 21 has a square
configuration which, as is well-known, provides a very efficient
electromagnetic coupling relationship with the winding 21. The
other portions of the stator core outside of the winding 21 need
not be as thick as the combined leg portions 16, and the optimum
thickness of the stator in all areas other than the leg portions
can be determined by techniques well known to those skilled in the
art from a knowledge of the leakage flux at the pole faces of the
stator core, the surface area of the rotor poles, the air gap
between stator pole pairs, and the unmagnetized transition region
between the adjacent north and south poles of the rotor.
A winding bobbin 19 comprised of any suitable material such as a
hardened plastic material is supported by the winding support legs
16. The energizing winding 21 is concentrically wound about the
bobbin and in the preferred embodiment is comprised of 6,000 turns
of 43 gage, copper wire having a total resistance of approximately
860 ohms. It should be understood, however, that the number of
turns and the wire gage used may be of any suitable number and type
depending on the number of stator pole pairs, the torque required,
and the operating voltage range. Electrical current is coupled to
the winding 21 via leads 23.
The end portions of the stator core passing outside of the winding
21 are separated to form an axial air gap 27 for the rotor 25. The
size of the air gap depends on the thickness of the rotor and the
DC magnetic stiffness desired. Thus, ordinarily it is desirable to
make the air gap large for manufacturing ease but, as will be seen
hereinbelow, the magnetic stiffness should not be too low so as to
prevent efficient operation of the motor. The axial air gap permits
the magnetic field generated by the stator to be directed onto the
rotor perpendicular to the rotor plane and complementing this, the
magnetic field generated by the rotor is directed to the stator
poles perpendicular to the plane of the surface of the stator
poles. This results in substantially less flux leakage and less
reluctance to the magnetic field generated by the stator.
Accordingly, the efficiency of the motor is materially
improved.
The rotor is a disc having a thickness of approximately 0.023
inches and consists of a low density material such as barium
ferrite in a rubber binder which is commonly sold under the trade
name Plastiform and which is relatively inexpensive in the sizes
required for the rotor. The residual induction value, i.e.,
retentivity of Plastiform, is 0.22 webers per meter.sup.2 which, as
will be seen hereinbelow, is of importance to the operating
characteristic of the motor of this invention. As shown in FIG. 2,
an annular ring about the outer periphery of the rotor is
permanently magnetized through the thickness of the rotor to form
an annular magnetic working area on both sides of the rotor. The
magnetized area includes truncated triangular sections called rotor
poles which are of alternately opposed polarity as can be most
conveniently seen in FIG. 3. The poles are positioned so that they
are contiguous to one another about the periphery of the rotor
thereby rendering the entire annular ring available for generating
alternately opposed magnetic fields. The rotor is mounted on an
axial shaft 29 for rotation with respect to the stator by any
suitable means known in the art. In the preferred embodiment there
are 16 rotor poles and the energizing winding 21 is excited with a
current having a frequency of 64 Hz. Accordingly, the rotor is
driven at 8 cycles per second.
The aforementioned synchronous motor is of exceedingly simple yet
rugged construction suitable for rapid mass production and for use
in vibrational environments such as in automotive vehicles. As will
be explained hereinbelow, since the rotor density is low, while at
the same time having a large magnetic working area, the ratio of
the moment of inertia of the rotor to the torque developed by the
motor is low, thereby rendering the motor capable of self-starting.
A simple no-back device cooperating with the gear train (not shown)
is employed to insure rotation of the rotor in the desired
direction. Such devices are very well-known in the art to which
this invention pertains.
The operation of the motor is according to well-known principles of
synchronous motors. Briefly, with the rotor positioned as shown in
FIG. 2 and assuming it is rotating counter clockwise, the stator
core passes a magnetic flux field through the rotor such that the
north magnetic pole 31 is attracted to the stator pole pair. At the
same time the south magnetic pole 33 is repulsed in the counter
clockwise direction away from the stator pole pair. A fraction of a
second later and after 1/16th of a complete rotation of the rotor,
the magnetic field in the stator is reversed and the south magnetic
pole 35 of the rotor is attracted to the stator pole pair and the
north magnetic pole 31 is repulsed in the counter clockwise
direction away from the stator. Thus, the stator pole is
continuously driven by the interaction of the alternate polarity
magnetic fields of the rotor and the alternating magnetic field in
the stator. It should be understood that a pulsating unipolar
magnetic flux field could also be generated in the stator. In such
a case, the rotor north pole 31 would be attracted and the rotor
south pole 33 repulsed when a unipolar pulse is coupled to winding
21. A fraction of a second later and after 1/8 of a complete
rotation of the rotor, the magnetic field in the stator is again
generated with the same polarity, hence north rotor pole 36 is
attracted toward the stator and south rotor pole 35 is repulsed
away therefrom in the counter clockwise direction. Since the rotor
is driven once every 1/8 of a revolution rather than every 1/16th
of a revolution, the movement, of the rotor will be less smooth
when excited by a unipolar pulsating magnetic field than when
excited with a typical AC flux field.
The developed torque required to self-start a permanent magnet
synchronous motor must be greater than the static friction torque
plus the stiffness torque due to the permanent magnet plus the
inertia torque of the rotor. The low density of the rotor material
obviously reduces the friction and inertia torque and the permanent
magnet stiffness torque can be adjusted to the appropriate value
depending on the specific use requirements of the motor. The
average torque that can be developed by such a motor is
proportional to the product of the magnetic field due to the
impressed current in the windings and that due to the permanent
magnets in the rotor. Both of these torques are dependent on the
characteristics and geometry of the magnet path through the rotor,
stator and the air gap separating the rotor and stator. Since the
rotor of this invention is thin and has a low moment of inertia and
yet has a large magnetic working area, the motor is able to develop
a large torque at low power input levels and at the same time
requires relatively little starting torque when compared with prior
art motors. The maximum torque required to self-start the
synchronous motor of this invention can be shown to be:
T.sub.r = 16 .pi. J f.sup.2 /P.sub.r (1)
where T.sub.r is the required torque, J is the moment of inertia of
the rotor, f is the frequency of the current coupled to the
energizing windings, and P.sub.r is the total number of rotor
poles. It thus can be seen that the moment of inertia J should be
held to a minimum in order to reduce the torque required for
self-starting.
The proper expression for the moment of inertia of the rotor shown
in FIG. 3 is:
J = D L.sub.r A.sub.r.sup.2 /2.pi. (2)
where D is the density of the rotor material, L.sub.r is the
thickness of the rotor magnet and A.sub.r is the total surface area
of one side of the rotor disc. Substituting equation (2) into
equation (1) the following equation is derived:
T.sub.r = 8 D L.sub.r A.sub.r .sup.2 f.sup.2 /P.sub.r (3)
Thus the maximum torque required for self-starting is directly
proportional to the density of the rotor, the thickness of the
magnetic poles, the square of the surface area of the disc, and the
square of the frequency of the excitation voltage.
The expression for the maximum torque that can be developed by the
synchronous motor of this invention is given as follows:
T.sub.d = P.sub.s P.sub.r (L.sub.g + L.sub.r) .phi..sub.s
.phi..sub.r /4 MoA.sub.p (4)
where T.sub.d is the maximum torque that can be developed by the
motor, P.sub.s is the number of stator pole pairs, L.sub.g is the
air gap length, .phi..sub.s is the peak value of the magnetic flux
in the air gap that is generated by the impressed current,
.phi..sub.r is the maximum net magnetic flux in the air gap
generated by the permanent magnets of the rotor, Mo is the
permeability of free space and A.sub.p is the cross sectional area
of a single stator or rotor pole. It should be noted that the
aforementioned formula is accurate provided that the stator iron
does not become saturated, the flux in the air gap varies
sinusoidally, and the gear train backlash of the associated clock
is such that the motor is brought to synchronous speed before any
load torque is reflected back to the rotor. In addition, it is
assumed that the stator pole faces have the same geometric
configuration as the rotor poles and that fringing effects are
neglected. These conditions are typical of present day clock gear
trains and of synchronous motors.
The flux expressions in equation (4) should be converted to
expressions of current in order for equation (4) to be meaningful
in terms of input power and efficiency. Thus, equation (4) can be
rewritten as:
T.sub.d = 0.16 P.sub.s NI A.sub.a R (L.sub.r /L.sub.r + L.sub.g)
(5)
where N is the number of turns in the energizing winding 21, I is
the maximum current coupled thereto, A.sub.a is the total annular
area of the permanent magnet poles, i.e., the magnetic working
area, and R is the residual induction value of the Plastiform rotor
material which is 0.22 webers per meter.sup.2. Since the developed
torque is proportion to the magnetic working area A.sub.a, it is
important that this area be made as large as possible such as by
making the sides of each magnetic rotor pole contiguous with its
neighbors.
Since the maximum average developed torque has to be equal to or
greater than the maximum average required torque, equations (3) and
(5) are equated to determine the required current.
I = 50D f.sup.2 A.sub.r.sup.2 (Lr + Lg)/P.sub.r P.sub.s A.sub.a R N
(6)
equation (6) can now be applied to the synchronous motor
illustrated in FIGS. 1-3 by assuming the following values for the
parameters of the equation:
P.sub.s = 1
P.sub.r = 16
L.sub.r = 10 .sup..sup.-3 meters
A.sub.r = 1.26 .times. 10 .sup..sup.-4 meters .sup.2
A.sub.a = 0.79 .times. 10 .sup..sup.-4 meters .sup.2
R = 0.22 weber/meter.sup.2
D = 3.7 .times. 10.sup.3 kilograms/meter .sup.3
f = 64 Hz
N = 6,000
The value of I required to self-start the synchronous motor is
found to be 10.48 milliamperes, and the output torque developed is
1.21 .times. 10 .sup..sup.-4 newton meters or 8.84 ounce inches.
Since the output power is the product of the output torque and the
angular speed of the rotor, the power output is computed to be 6.07
milliwatts.
Now the input power can be computed by the following formula:
P.sub.I = I.sup.2 R + P.sub.c + P.sub.o (7)
where R is the total resistance of the winding which is
approximately 860 ohms, P.sub.c is the power loss in the core due
to hystersis and eddy currents and is estimated to be approximately
50 microwatts, and P.sub.o is the power output. Accordingly, the
power input can be computed and is
P.sub.I = 6.07 + 47.6 + 0.05 = 53.72 milliwatts
The efficiency can now be computed and is:
E = P.sub.o /P.sub.in 100% = 6.07/53.72 100% = 11.3% (8)
As can be seen the synchronous motor not only can develop
sufficient torque for self-starting, but the efficiency thereof is
a substantial improvement over the 1% efficiency levels of prior
art simplified synchronous timer motors. If the motor is not
required to be self-starting, as for example, in the case where the
motor is started by hand, the high starting torque is not required
and hence very low power operation is possible.
It can be seen from equation (6) that if the number of stator poles
is increased, the maximum input current required is reduced.
Assume, for example, that the number of stator poles is increased
to eight. Applying the above formula, the maximum required input
current can be found to be 1.31 milliamperes and the developed
torque can be found to be 8.84 ounce-inches. Since the power output
is the product of torque developed and the angular speed of the
rotor, the power output P.sub.o is found to be 6.07 milliwatts
which is the same as in the case where the stator has only one pole
pair. Assuming the coil resistance to be 860 ohms, the input power
to supply the copper losses is 0.744 milliwatts and the core losses
will be approximately 10 times higher than in the one stator pole
case. Thus the total input power P.sub.I can be computed by
equation (7) and is 7.31 milliwatts. The efficiency according to
equation (8) is:
E = P.sub.o /PI 100% = 6.07/7.31 (100) = 83.1%
Thus by increasing the number of stator poles, the efficiency of
the synchronous motor is substantially increased.
Refer now to FIG. 4 which is a partial end view of the stator
showing the configuration of the stator pole face with respect to
the magnetized portion of the rotor. As shown the stator portion 18
is in the form of a truncated triangle. this configuration most
nearly matches the configuration of the permanently magnetized pole
faces of rotor 25. The upper leg portion 18 of the stator extends
downward to the lower leg portion 16 thereof with the windings 21
not shown. The leg 16 of plate 17 of the stator is shown and as
aforementioned is spot welded to plate 15 to form a unitary stator.
It should be understood that while the aforementioned equations
were developed with respect to a stator pole having the
configuration shown in FIG. 4, the stator poles, also, can have a
rectangular configuration as illustrated most clearly in FIG. 2.
The rectangular pole face construction requires fewer steps in
manufacturing the stator thereby reducing the cost of the motor
while at the same time the characteristics of the motor including
efficiency are not substantially adversely affected by such a
modification in the stator pole configuration.
Refer now to FIG. 7 where there is shown a schematic diagram of a
drive circuit for providing AC energization to the winding 21 of
the synchronous motor. The circuit is comprised of three
fundamental parts, namely, a crystal controlled oscillator designed
by the numeral 47, a divider circuit 49 and a drive circuit 51. DC
power is coupled to the circuit via resistor 43 which provides
transient current protection for each of the three components of
the circuit. A Zener diode 45 is coupled between the low voltage
end of resistor 43 and a reference potential such as ground. A
second DC source 53 is coupled to the divider and drive circuits
for providing the appropriate bias potential thereto.
The oscillator circuit includes a quartz crystal 55 which is
designed to oscillate at 262,144 Hz. Quartz crystals are well-known
and are readily available commercially. The crystal 55 is connected
at one side thereof to the input of an amplifier 57 and the other
side thereof is coupled to the output of the amplifier via a
variable capacitor 59. The input of amplifier 57 is also connected
to reference potential via a fixed capacitor 61 and the output of
the amplifier is coupled to reference potential via fixed capacitor
63. A biasing resistor 65 is connected between the input and output
terminals of amplifier 57 and biases the amplifier 55 in its active
region to initiate oscillation of oscillator 47. Variable capacitor
59 operates to vary the resonant frequency of the crystal
oscillator thereby varying the frequency at the output of amplifier
57. The output of the amplifier 57 which is 262,144 Hz is connected
to a buffer amplifier 67 which preferably has a high input
impedance so that operation of the divider stage 49 does not
adversely affect the frequency of the output of the oscillator 47.
The output (C-MOS) buffer amplifier 67 is connected to divider 49
which includes a plurality of binary divider stages. In the
preferred embodiment the divider 49 includes twelve serially
connected flip-flops which divide the output of the crystal
oscillator down to 64Hz. The output of the divider is connected to
a drive circuit 51 which provides an output current on the order of
several milliamperes for energizing the windings 21. The divider
circuit 49, the drive circuit 51, buffer amplifier 67 and the
amplifier 57 are formed on an integrated circuit chip commonly
known as a complementary metal oxide semi-conductor C-MOS) by
integrated circuit techniques well known in the art. The circuit
illustrated in FIG. 7 provides not only a highly stable 64 Hz
output for driving windings 21 but also requires very little power
from the DC source of energy.
Refer now to FIG. 5 where there is shown a cross sectional view of
a multi-stator pole self-starting synchronous motor. The stator
includes a core portion comprising a pair of legs 71 and 73 with a
cylindrical connecting arm 75 separating each of the legs. The
connecting arm 75 consists of a soft iron material and has a hole
therethrough through which a bolt extends for securing the
connecting arm to the legs 71 and 73. The legs 71 and 73 are bent
inwardly toward each other proximate the rotor 77 with each of the
legs having aligned holes for permitting the rotor spindle or shaft
89 to pass therethrough. A bushing 79 is positioned in each hole. A
pair of complementary stator pole pieces each having eight pole
faces thereon are mounted on each bushing with the pole faces of
the pole pieces being directed toward each other as shown in FIG.
5. A pole piece is shown in perspective in FIG. 6. A hole 81
extends through the center thereof into which is positioned a
bushing 79. At the external periphery of the pole piece are a
plurality of pole faces 84 extending upwardly away from the base
portion of the pole piece. Each of these faces are separated by a
notched portion 83. The pole faces, as shown, take the form of a
truncated triangle having the same general configuration as the
magnetized portion of the rotor shown in FIG. 4.
The stator is supported by means of a pair of brackets 85 which
consist of a non-magnetized material. The pole pairs 78 are
separated or spaced with respect to each other by means of a pair
of spacers 87 positioned between the legs 71 and 73 of the stator
and are secured in place by a pair of bolts extending through the
brackets 85, the legs 71 and 73, and the spacers 87. A rotor 77 is
positioned between the pole pairs 78 with an axial air gap
separating the rotor from the pole pairs. The rotor is mounted on a
spindle 89 which is journaled for rotational motion in the frame of
the motor 91. Axial bearings 93 permit relatively frictionless
rotational movement with respect to brackets 85 and axial bearings
94 permit relatively frictionless movement of the spindle 89 with
respect to bushings 79.
In operation the multi-stator rotor of FIG. 5 attracts and repels
the rotor poles in the same manner as the single stator pole rotor
except that more stator poles are now attracting and repelling the
corresponding rotor poles thereby generating a larger torque
output.
The synchronous motors described herein are particularly well
adapted for driving automobile clocks since they are of simple yet
rugged construction thereby rendering the motors amenable to mass
production techniques. Further, since the synchronous motors
provide direct rotational energy to a clock gear train, the
intermittent reciprocal to rotational motion converting mechanism
normally required in automobile clocks which is susceptible to
ambient temperature variations and shock is not required thereby
providing a more accurate automobile clock. Finally, the increased
efficiency of these motors permits their use in automobiles without
concern that the battery might be drained of energy by the motor.
While several embodiments of the self-starting synchronous motor
have been described, it is within the contemplated scope of this
invention that numerous changes can be made in the embodiment
described without departing from the spirit and scope of the
invention as defined by the appended claims.
* * * * *